public class Test {
    int a = 10;//自动装箱
    Integer b = new Integer(20);//手动装箱
    Integer c = 20;
    Integer d = Integer.valueOf(100);

    public static void main(String[] args) {
        Integer a = 20;
        int b = a;//自动拆箱

        float f = a.floatValue();
        long l = a.longValue();

        System.out.println(b);
        System.out.println(f);
        System.out.println(l);
    }

}
